Much of modern audio recording and listening is based on stereophonic sound, commonly called “stereo” or “surround sound.” Stereophonic sound is the reproduction of sound, using two or more independent audio channels, through a symmetrical configuration of loudspeakers (speakers), in such a way as to create a pleasant and natural impression of sound heard from various directions, as in natural hearing. A stereo system offers the capability of reproducing at least some “sense of space,” thus providing a listener with a more realistic reproduction of an original acoustic performance. Employing additional audio channels may enhance that capability. In popular usage, stereo usually means two-channel sound recording and sound reproduction using data for more than one speaker simultaneously. In technical usage, “stereo” or “stereophony” means sound recording and sound reproduction that uses stereographic projection to encode the relative positions of recorded objects and events. A stereo system can include any number of channels, such as the surround sound 5.1- and 6.1-channel systems. However, in common use it refers to systems with only two channels.
Normally, preparation of audio material for commercial distribution is done in a special listening environment, such as a mixing studio or mastering studio. The listening environment is typically equipped with audio speakers. An audio engineer can make many types of sonic adjustments while listening to the sound coming out of the speakers. One very important adjustment that can be made is called “sound separation,” stereophonic sound attempts to create an illusion of location for various instruments within the original recording. The recording engineer's goal is usually to create a stereo “image” with localization information.
When playing back stereo recordings, the best results are obtained by using two speakers, located in front of and equidistant from the listener, with the listener located on the center line between, and facing, the two speakers. The listener's left ear has a more direct path to the left, and the right ear has a more direct path to the right speaker. When a stereophonic recording is heard through loudspeaker systems rather than headphones, each ear hears sound from both speakers. As in the case of a live musical performance, both ears react to sounds from all directions. Much of the sense of space is due to the relative amount of sound received by the left and right ear. An audio engineer may and often does use more than two microphones, sometimes many more, mixing the microphone signals down to two tracks. Typically, each audio stereo channel carries some of its own individual sound and also some sound that is common to both channels.
If all the sound in both channels is common, the system becomes a monophonic system resulting in loss of spatial perception. If the channels are totally separated, for example, when a listener is using headphones, proper spatial perception is lost. The resulting effect is distorted spatial perception. Headphones, therefore, introduce additional, unintended separation between the audio sound heard by listener's left and right ears. A signal out of a left speaker is intended to reach both ears, but with headphones, the same signal reaches only the left ear. Similarly, a signal out of a right speaker is intended to reach both ears, but with headphones, the same signal reaches only the right ear. Therefore, headphones result in added unintended stereo separation.
Significant differences between a recording environment, for example, a music production studio loudspeaker setup and a home listening environment setup, can also cause alterations between the intended spatial perception and the actual spatial perception in the home listening environment. Many home listening environments are set up in a way that is far from perfectly emulating an ideal listening studio stereo setup. Many factors, such room size, doors, windows, furniture location, etc., may cause a home listener to be located in a less then symmetrical listening position relative to the speakers. Thus, the spatial perception intended by a recording engineer in a recording (e.g., production studio) environment can be distorted in a home listening environment due to the differences between the studio and the home listening environments.
Therefore, there is a need for a system and method that allow a listener to control the composition of stereo separated audio signals in a sound entertainment system so as to enhance the listener's enjoyment by compensating for the distortions caused by the differences between recording and listening (e.g., home) environments.